
CHAPTER. Xx iy 
SOILS AND SUBSOILS 
Agents of Disintegration ; Insolation and Deflation; Rain; Frost; Life. 
Weathering of Rocks. The Soil-cap. Classification of Soils—I. 
Bed-rock Soils, their Varied Character ; Soils derived from Igneous, 
Metamorphic, and Derivative Rocks. II. Drift Soils; Glacial, 
Alluvial, and A£olian Soils. 
Rock-disintegration.—Subsoil has already been defined as 
an unconsolidated heterogeneous aggregate of disintegrated 
rock material, and soil as essentially the same, with the 
addition of organic matter.. Both are the resulivereiae 
operation of various epigene agents, and are therefore 
properly included among derivative rocks. Everywhere 
throughout the world we meet with these superficial 
accumulations. As might have been expected, they vary 
in character according to the conditions under which they 
have been formed, and the nature of the rocks from which 
they have been derived. In some regions, for example, 
they consist largely of angular and subangular detritus, while 
in other places they may consist mainly of sand or of clay, 
as the case may be. In high latitudes and in mountainous 
lands the soil-cap is usually very stony; in lower latitudes 
and over plains and gently undulating tracts its ingredients 
are commonly finer grained. In most regions, however, 
arable soils are composed essentially of insoluble quartz-sand 
and clay, in ever-varying proportions, throughout which are 
disseminated larger or smaller percentages of organic matter 
and of certain more or less soluble ingredients, such as iron- 
oxides, magnesia, lime, soda, potash, etc. 
In preceding pages, frequent reference has been made to the 
alterations and transformations of minerals and rocks induced 
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